Rotary electric machine, and in particular motor vihicle alternator, comprising a stator elastically mounted in a heat-conductive resin

ABSTRACT

The invention proposes a rotary electrical machine ( 10 ), especially a motor vehicle alternator, of the type comprising a stator ( 12 ) of generally cylindrical annular form, which is arranged in a casing ( 14 ) comprising a rear portion ( 16 ) and a front portion ( 18 ), of the type in which the outer axial face ( 24 ) of the stator ( 12 ) and the inner axial face ( 30 ) of the casing ( 14 ) delimit an annular radial space ( 32 ), and of the type in which the stator ( 12 ) is suspended elastically within the casing ( 14 ), characterized in that at least part of the annular radial space ( 32 ) contains thermally conductive resin ( 50 ) which is deformable axially and interposed radially between the casing ( 14 ) and stator ( 12 ), so as to effect radial mechanical decoupling between the stator ( 12 ) and casing ( 14 ) and so as to dissipate heat energy from the stator ( 12 ) to the casing ( 14 ).

[0001] The present invention relates to a rotary electrical machine.

[0002] In particular, the invention relates to an alternator or analternator-starter motor which is used for supplying the electricalcircuit of a motor vehicle with energy.

[0003] The invention relates to a rotary electrical machine of the typecomprising a rotor, a stator of generally cylindrical annular form whichis arranged within a casing comprising a rear portion and a frontportion, which are joined together along a junction plane at rightangles to the axis of the rotor of the machine, of the type in which theexternal axial face of the stator delimits, with the internal axial faceof the casing, an annular radial space, and of the type in which thestator is clamped axially between the opposed radial engagement surfaceswhich are formed in each of the two portions of the casing, with atleast one elastically deformable element being interposed and compressedaxially between each of the two engagement surfaces and a portion of thefacing annular radial end face of the stator.

[0004] A rotary electrical machine of this type is described in thedocument FR-A-2 727 807.

[0005] In that type of rotary electrical machine, the stator is not indirect contact with the casing, but it is insulated from it byelastomeric pads and by air. In consequence, the stator is isolated fromthe vibration point of view, but it does not evacuate enough of the heatwhich is produced when the machine is working, and the workingtemperature then rises above the values that can be tolerated by thecomponents of the machine.

[0006] In addition, the pads and seals used in that machine to act asvibration dampers are of relatively complex forms, which increases thecost of manufacturing and assembling the machine.

[0007] In the case where the seal used is of the type having an L-shapedcross section, fitting it on the stator is less easy to do within thecycle time of a quantity production process.

[0008] The invention aims to propose an improvement in such a type ofrotary electrical machine which does not have the above mentioneddrawbacks.

[0009] With this in view, the invention proposes a rotary electricalmachine of the type defined above, characterised in that at least partof the radial annular space contains elastically deformable thermallyconductive resin which is interposed radially between the casing and thestator, whereby to effect radial mechanical decoupling between thestator and casing, and whereby to dissipate heat energy from the statorto the casing.

[0010] In accordance with further features of the invention:

[0011] only the front portion of the casing contains the thermallyconductive resin;

[0012] an elastically deformable flat annular seal is interposed axiallybetween the, annular front radial end face of the stator and theengagement surface formed in the front portion of the casing;

[0013] a set of elastically deformable pads are spaced apartcircumferentially and compressed axially between the rear annular radialend face of the stator and a portion of the engagement surface definedin the rear portion of the casing;

[0014] each pad includes a positioning lug in the form of a dovetailwhich is received axially in a complementary seating formed in the rearportion of the casing.

[0015] Thanks to the invention, the elastically deformable flat annularseal and the set of elastically deformable pads are protected due to thepresence of the thermally conductive resin.

[0016] In addition, the alternator is simplified because a flat annularseal replaces an L-shaped annular seal of the prior art. The pads aresimplified.

[0017] The pads and the seal, in particular, provide axial vibrationdamping.

[0018] The resin provides radial vibration damping.

[0019] Thanks to the resin, heat is evacuated efficiently so that it ispossible to increase the power output of the alternator.

[0020] Thus in one embodiment, the volume of the winding of the rotor isincreased.

[0021] In one embodiment, the rectifier unit is so configured that itgives this power increase and evacuates heat well.

[0022] In one embodiment, the conductor elements of the stator are cladin a linking layer to improve heat evacuation.

[0023] The invention also provides an alternator, especially for a motorvehicle, having at least one of the foregoing features.

[0024] Further features and advantages of the invention will appear on areading of the following detailed description, for an understanding ofwhich reference will be made to the attached drawings, in which:

[0025]FIG. 1 is a half view in axial cross section of an alternator madein accordance with the features of the invention;

[0026]FIG. 2 is a perspective view showing a damping pad in thealternator of FIG. 1;

[0027]FIG. 3 is a scrap view in transverse cross section, showing themounting of the damping pad of FIG. 2 in a complementary seating in thecasing of the alternator;

[0028]FIG. 4 is a detail view from FIG. 1, showing that portion of theannular radial space in the stator that contains the thermallyconductive resin;

[0029]FIG. 5 is a view similar to FIG. 1, showing the positioning of theflat annular seal in the front portion of the casing of the alternator;

[0030]FIG. 6 is a view similar to FIG. 1, showing the positioning of thestator in the front portion of the casing of the alternator, before thethermally conductive resin is caused to flow into the radial annularspace and before the rear portion of the casing is fitted;

[0031]FIG. 7 is a view in axial cross section of the alternator of FIG.1 equipped with the front portion of the casing from FIG. 6;

[0032]FIG. 8 is a large scale view in axial cross section of a windingof conductor elements which are coated by being clad in a connectinglayer;

[0033]FIG. 9 is a view similar to FIG. 8 after the connecting layer hasfilled the interstices that exist, so joining the conductor elementstogether;

[0034]FIG. 10 is a view in cross section of the stator of FIG. 7 placedin a forming tool;

[0035]FIG. 11 is a view similar to FIG. 10, in which the forming toolhas deformed the ears of the stator;

[0036]FIG. 12 is a perspective view of the forming tools for the windingof the rotor of FIG. 7;

[0037]FIG. 13 corresponds to FIG. 12 but is in axial cross section;

[0038]FIG. 14 is a partial view in perspective, of a rectifier unitarranged to be mounted on the rear portion of the alternator of FIG. 7;

[0039]FIG. 15 is a perspective view of a heat dissipater of therectifier unit of FIG. 14;

[0040]FIG. 16 is a top plan view of the heat dissipater of FIG. 15;

[0041]FIG. 17 is a top plan view of an insulating intermediate plate ofthe rectifier unit of FIG. 14;

[0042]FIG. 18 is a perspective view of a cap for covering the rectifierunit of FIG. 13.

[0043] In the following description, identical or similar componentsshown in the various drawings are designated by the same referencesigns.

[0044] An orientation from back to front along the axis X-X of thealternator will be arbitrarily used, corresponding to a downwardorientation in FIG. 1 and an orientation from right to left in FIG. 7.The axis X-X is both the axis of axial symmetry and the axis of rotationof the alternator.

[0045]FIG. 1 shows a motor vehicle alternator 10 which consistsessentially of a stator 12 mounted in a casing 14 which comprises a rearportion 16 and a front portion 18, together with a claw-type rotor (notshown in FIG. 1).

[0046] In the conventional way, the rotor is mounted for rotation withina cylindrical annular chamber defined within the stator 12.

[0047] The stator 12 surrounds the rotor and comprises a body consistingof a stack of grooved laminations carrying a multiphase armaturewinding. The body has a generally cylindrical annular form delimited bytwo annular radial terminal surfaces, namely a rear surface 20 and afront surface 22, and by a cylindrical outer surface 24. The grooves inthe body are, in the known way, of blind and half closed form. Thesegrooves are open at the inner periphery of the body of the stator.

[0048] The two portions 16 and 18 of the envelope or casing 14 thatreceives the stator 12 are two moulded and machined members, each ofwhich receives a bearing (not shown in FIG. 1) for mounting the shaft ofthe rotor for rotation therein. In FIGS. 1 and 7 the portions 16, 18 aremetallic, being made of aluminium.

[0049] The two portions 16, 18 of the casing 18 are commonly called therear bearing 16 and front bearing 18 respectively. Each of theseportions has a machined annular radial terminal face 26, 28, and thesefaces define a junction plane P of the two portions 16, 18 of the casing18, along which they are held axially by means of a set of four clampingscrews (not shown in FIG. 1), which are spaced apart circumferentiallyat regular intervals about the axis X-X of the alternator 10.

[0050] The outer cylindrical surface 24 of the stator 12, with the innercylindrical surface 30 of the casing 14, delimits a radial annular space32.

[0051] The stator 12 is suspended elastically within the casing 14,consisting of its two portions 16, 18, for reduction of noise,especially magnetic noise.

[0052] In accordance with an arrangement known in the state of the art,the stator 12 includes at the rear a set of elastic pads 34 in the formof blocks which, in this example, are four in number and are spacedapart circumferentially at regular intervals about the axis X-X, in sucha way that they are interposed axially between a portion of the radialannular rear end face 20 of the stator 12 and a radial annular rearengagement surface 36, which are formed in facing relationship in theportion, in the form of a cylindrical sleeve, of the rear portion 16 ofthe casing 14.

[0053]FIG. 2 shows one example of the pad 34, which is simplified ascompared with that in the prior art.

[0054] Each pad 34 in this example is a block having a general form of arectangular parallelepiped defining two parallel and opposed engagementfaces 35 and 37, each of which bears respectively against a facingportion of the radial annular rear end face 20 of the stator 12 andagainst the radial annular engagement surface 36 which is machined inthe rear portion 16 of the casing 14.

[0055] Each pad 34, in the form of a rectangular block, is extendedlaterally by a positioning lug 38 of dovetail form which has two axialedges 40, 42.

[0056] The positioning lug 38 is received axially in a complementaryseating 44 formed in the cylindrical skirt portion of the rear portion16 of the casing 14, as can be seen in FIG. 3.

[0057] The positioning lug 38 is formed integrally in one piece.

[0058] The stator 12 includes at the front an elastically deformableannular flat seal 46, which is interposed axially between a portion ofthe radial front annular end face 22 of the stator 12 and an annularradial engagement surface 48, which is formed in facing relationship inthe cylindrical skirt portion of the front portion 18 of the casing 14.

[0059] The flat seal 46 advantageously replaces a seal of L-shaped crosssection in the prior art.

[0060] The pads 34 and the annular seal 46 are made of axiallycompressible material, for example elastomer or rubber.

[0061] After being tightened up, and as is shown in FIG. 1, the pads 34and the annular seal 46 are compressed axially between the annularradial end faces 20, 22 of the stator 12 and the engagement surfaces 36,48 associated with the portions 16, 18 of the casing 14, the annular endsurfaces 26 and 28 of the casing 14 being gripped in contact on thejunction plane P.

[0062] In accordance with the features of the invention, and as can beseen in the detail view in FIG. 4, the annular radial space 32 containsresin 50, or adhesive, which is elastically deformable and conductive ofheat, and which is interposed radially between the outer cylindricalsurface 24 of the stator 12 and the inner cylindrical surface 30 of thefront portion 18 of the casing 14.

[0063] Preferably, only the lower portion, or front portion, of theradial annular space 32 is filled with the resin 50. The resin is thusspaced away from the rectifier unit of FIG. 14, and is therebyprotected.

[0064] The resin 50 must be able to deform elastically in the radialdirection, so as to give mechanical radial decoupling between the stator12 and casing 14.

[0065] It is also clearly possible to envisage that the resin 50 beplaced on the rear portion of the annular radial space 32.

[0066] Thus, the resin 50 damps radial vibrations emitted by the stator12 during its operation, so as to prevent them from being transmitted tothe casing 14 and emitting noise.

[0067] The resin 50 also improves the dissipation of thermal energyemitted by the stator 12 towards the casing 14. In this connection, thethermally conductive resin 50 conducts heat better than air or theelastomeric materials of the pads 34 and seal 46. It therefore improvesthe evacuation of heat by the alternator 10 from the stator 12 to thecasing 14.

[0068] The said resin simplifies the pads 34 and enables a flat seal 46to be provided. The pads and the seal damp out axial vibrations.

[0069] The assembly of the various components of the alternator 10 iscarried out in the following way.

[0070] The flat annular seal 46 is positioned in the front portion 18 ofthe casing 14, with the open face of the latter being preferablyoriented upwards as in FIG. 5.

[0071] The stator 12 is then put in place in the front portion 18, withits annular front radial end face 22 in axial engagement against theseal 46.

[0072] Preferably, a centring tool of known type is used to position thestator 12 coaxially with the bearings of the casing 14.

[0073] In addition, the four pads 34 are positioned in the correspondingseating 44 of the rear portion 16 of the casing 14.

[0074] To this end it is possible to arrange that the transversedimensions of the positioning lugs 38 shall be slightly greater than thewidth of each seating 44, so as to maintain the lug 38 in position inthe seating 44 by slight compression of the material of the lug 38.

[0075] Thermally conductive resin 50 or adhesive material is then flowedinto the radial annular space 32 until the depth of the resin 50 reachesfor example three quarters of the depth of the cylindrical skirt of thefront portion 18 of the casing 14.

[0076] It will be noted that the flat annular seal 46 hermetically sealsthe front axial end of the radial annular space 32, which prevents theresin 50 from flowing out of the radial annular space 32, for exampletowards the front of the casing 14.

[0077] The resin 50 is then polymerised in such a way that it will beaxially deformable and no longer flow.

[0078] It will be noted that after being polymerised, the resin 50centres the stator 12 and immobilises it radially.

[0079] The rear portion 16 of the casing 14 is then put in place on thefront portion 18 with the engagement faces 34 of the pads 34 in contactagainst the radial annular rear end face 20 of the stator 12, so as toachieve the final assembly shown in FIG. 1.

[0080] In various modified embodiments (not shown) of the invention, theresin 50 may be injected into the radial annular space 32 using severalknown techniques.

[0081] For example, an injection hole may be provided in the cylindricalskirt of one of the portions 16, 18 of the casing 14, to enable resin 50to be injected after the rear portion 16 has been mounted on the frontportion 18.

[0082] This invention may of course also be used for motor vehiclealternators of the type described above but having a wound stator, withconductors of large diameter in the form of bars. Such a stator windingis described for example in the document WO92/06257. Conductors in theform of bars well fill the slots of the stator body, and are generallyin the form of hairpins, preferably of round or square or rectangularcross section. Conductors in the form of bent bars may for example, withadvantage, replace the hairpins.

[0083] Thanks to the invention, a wound stator of this type with largeconductors in the form of bars is easy to cool.

[0084] The arrangement of the stator in the casing 14 according to theinvention is applicable with advantage to motor vehicle alternators orto those electrical machines of the “alternator-starter” type which areknown per se and which are adapted to operate alternately as startermotors and as alternators. For more details, reference should be made toApplication FR-00 03131 filed on Mar. 10, 2000.

[0085] Thanks to the invention it is possible to increase the power ofthe alternator because the thermally conductive resin evacuates heat sowell.

[0086]FIG. 7 shows the compact alternator 10 with internal fans 102,104.

[0087] This alternator, which in this example is of the multiphase type,consists mainly, as in FIG. 1, of a casing 14 consisting of two portions16, 18 with openings for flow of air. The casing 14 carries, as in FIG.1, two internal main members which consist of the stator 12 and rotor13, as described for example in the document U.S. Pat. No. 527,605(EP-B-O 515 259), to which reference should be made for more detail.

[0088] The stator 12 surrounds the rotor 13, which is fixed to a shaft15, on the rear end of which two slip rings 17 are fixed, while a pulley(not given a reference numeral) is fixed to the front end of the shaft15. This pulley is arranged to receive a belt which is part of a motiontransmitting device driven by the internal combustion engine of themotor vehicle. The axis X-X is the axis of the shaft 15.

[0089] The stator 12 comprises a body 19, which in this example consistsmainly of an axial stack of transverse soft iron laminations. Asmentioned above and as is known per se, each of the laminations of thestator 12 has notches to define slots which in this example are axial.These slots, one of which can be seen partly at 25 in FIGS. 8 and 9, areopen at the outer periphery of the body 19, which is of cylindricalform.

[0090] The slots extend radially outwards and receive electricalconductive axial tails of an electrical armature winding 23. The slotsare half closed on the inside, as can be seen for example in thedocument FR-A-2 603 429.

[0091] The electrical winding 23, which can be seen on a larger scale inFIGS. 8 and 9, consists, for each phase of the alternator, for exampleof the spiral winding of an electrically conductive wire, which is acopper wire here and which is coated with at least one layer ofelectrically insulating material 136, which is for example a polyesterconsisting of two layers, one of which is of the polyimide type and theother of the polyamide imide type.

[0092] An electrically insulating leaf 74 is interposed in each slot 25between the electrical winding 23 and the body 19 of the stator 13.

[0093] This leaf 24, which is immobilised in a way to be described laterherein in order to reduce noise and the sound level of the alternator10, enables the dangers of short circuiting between the winding 23 andbody 19 to be reduced or eliminated.

[0094] The operation of winding the electrically conductive wiretherefore results in the winding 23 comprising, in each slot 25, abundle of electrical conductor elements 134 which pass axially throughthe slots 25 and are extended outside the body 19 of the stator 12 byjunction tails, which form ears 39 that project on either side of thebody 19 as shown in FIG. 7.

[0095] In another version, hairpins of circular or rectangular crosssection are used, being mounted in the axial slots 25 of the stator 12as described in the document WO-92/06527. In a further version, fourelectrically conductive elements are mounted radially, beingsuperimposed on each other in each slot.

[0096] The inductor rotor 13 in this example is a claw-type rotor of theLundel type, which consists of a cylindrical electrical winding 62 whichis mounted between two metal plates 64 and 66, each of which includesclaws 68 and 70 respectively, which extend axially towards the otherplate 66 and 64. Each assembly of plate and claws constitutes a polewheel, of magnetic steel in this example. A core 67, which in thisexample is also of magnetic steel, is interposed axially between theplates 66, 64 to carry the winding 62. The core 67 is of annular formand is oriented axially, being in this example in the form of a thickannular ring. The core 67 is separate from the pole wheels, so as tofacilitate winding of the electrically conductive element on the core 67without the claws 68, 70 interfering. Each pole wheel is fixed on theshaft 15 by means of knurled portions of the shaft, one of which servesfor fastening of the core 67. The claws 68 and 70 are offsetcircumferentially from each other so that a claw 68 of the plate 64 isinterposed between two adjacent claws 70 of the plate 66 and vice versa.The claws have chamfers for reducing magnetic noise. For more details,reference should be made to the document EP-B-O 515 259. These chamfershave not been given reference numerals, in the interests of simplicityin FIG. 7.

[0097] The alternator in this example is, like that in the documentEP-B-O 515 259, arranged with internal ventilation, each plate 64, 66carrying a fan 102, 104 respectively adjacent to the portion 16, 18concerned of the casing. Each portion 18, 16 of the casing 12 hasopenings for flow of air, and carries a central bearing in the form of aball bearing 105, 106 respectively, to support the front and rear endsrespectively of the shaft 15. Thus, one of these portions 16, 18 iscalled the front bearing (i.e. the one adjacent to the pulley), whilethe other is called the rear bearing. It will be noted that the saidpulley is secured by means of a nut on the threaded front end of theshaft 15. In the upper part of FIG. 7, a spacer of L-shaped crosssection is interposed between the inner ring of the bearing 105 and thepulley. In the lower part of FIG. 7, the spacer is incorporated in thepulley, which reduces axial size still further.

[0098] The bearings 16, 18 are of hollow form, and each of them has abase in the form of a radial plate oriented transversely with respect tothe axis X-X of the alternator, and at their outer periphery they havean axially oriented annular flange, each of which includes thecorresponding machined radial annular end face 26, 28 which delimits thejunction plane indicated by the reference P in FIG. 1.

[0099] Each axially oriented flange is joined at its other axial end tothe transversely oriented radial plate which carries the central ballbearing 105, 106 concerned. In a known way, each radial plate and eachflange has openings for circulation of air. In FIG. 7 there can be seensome of the openings formed in the radial plates of the bearings 16, 18,and two openings in the peripheral flanges of the bearings 16, 18 areindicated in broken lines.

[0100] The openings in the flanges are located facing the ears 39.

[0101] The fans 102, 104 are located radially inwards of the ears 39,being fixed, for example by spot welding, to the plate 64 and plate 66respectively. These fans 102, 104, fixed to the rotor 13, have bladeswhich are preferably spaced apart at irregular intervals to reducenoise, and are in this example of the centrifugal type. In this way, airis aspirated and passes through the openings in the radial plates so asto be passed through the openings, which in this example are of oblongform, in the peripheral flanges.

[0102] The fans may have two sets of blades in the manner described inthe document FR00 08549 filed on Jun. 30, 2000.

[0103] More precisely, the second set of blades is shorter than thefirst set of blades, and at least one second blade is interposed betweentwo consecutive blades of the first set of blades.

[0104] For more detail, reference should be made to the said document.All the versions in that document may be envisaged. Thus a cover platemay overlie the first set of blades.

[0105] The ears 39 are thus well cooled, as are the rectifier unit 1,the voltage regulator which is part of the alternator 10, and the ballbearings 105, 106.

[0106] The rear bearing 18 carries a unit 1 for rectifying thealternating current produced by the winding 23 of the stator 12 which inthis example is three-phase, together with a brush carrier whichco-operates with the slip rings 17. The unit 1 converts the alternatingcurrent produced by the winding 23 into uni-directional current forrecharging the battery of the vehicle and supplying the power consumerssuch as the lighting apparatus, the air conditioning apparatus etc.

[0107] In the known way, the slip rings 17 are connected to the ends ofthe winding 62 of the rotor 13 through wire connections passing behindthe fan 104, as can be seen in FIG. 7.

[0108] A protective cap 27 is also provided, and is formed with openingsin a manner to be described later herein, for circulation of air.

[0109] The cap 27, which in this example is of plastics material,overlies the brush carrier which is connected in the known way to avoltage regulator 116, and the rectifier unit which includes diodes.

[0110] The brushes of the brush carrier are in frictional cooperationagainst the slip rings 17. The regulating device limits the voltagesupplied by the stator, in particular to protect the battery.

[0111] The bearings 16, 18 include lugs for fastening them on a fixedpart of the vehicle, and are fastened together, in this example with theaid of screws one of which can be seen at 29 in FIG. 7. The alternatorof the vehicle is thus connected electrically to earth via its bearings16, 18.

[0112] In another version, the radial plates of the bearings areinclined axially.

[0113] In a further version, the fan 102 is omitted, given that the rearfan is more powerful.

[0114] In general terms, the alternator includes at least one internalfan 13 fixed to the rotor and located inside the casing 14 under an ear39, in such a way that the winding 23 is well cooled and the alternatoris of high power while being compact, especially in the axial direction,and is also quiet.

[0115] In another variation, a single fan is arranged on the outside, inthe region of the pulley.

[0116] The resin 50 according to the invention provides the facility forevacuating more heat through the metallic bearings 16, 18, which in thisexample are of aluminium, and this enables the power from the alternatorto be increased, in particular by increasing the volume of the winding62 in a manner to be described later herein. This increase in powermakes it necessary to configure the rectifier unit 1 and the windings 23and 62 in a way which will be described below.

[0117] Thus, in accordance with one feature, it is proposed, for thewindings 23 and 62 of the stator 12 and rotor 13 respectively, to makeuse of an electrically conductive wire, in this example of copper, whichis spiral wound. The conductive wire is, as mentioned earlier herein,pre-coated with a layer 136 of electrically insulating material which isclad in a layer 72 for connection or fastening, and which includes atleast one linking material 73 which links together the coatedelectrically conductive elements 134 adjacent to the bundle of thewinding 23.

[0118]FIG. 8 is a partial transverse cross section of an electricwinding 23 of a stator 13 made in accordance with this feature. In thisFigure, a plurality of electrically conductive elements 134 can be seen,which are formed by winding the conductor wire to make the winding 23.

[0119] In accordance with another feature, the electrically insulatingleaf 74 comprises an electrically insulating structural element 174,such as paper or insulating fabric, at least one of the faces of whichis at least partially coated with a linking material 76. For example,only the face which faces towards the turns of the winding 23 is atleast partly coated with a linking material 76. Preferably, both facesof the structural element are coated with a linking material 76, thisbeing chemically compatible with the first linking material.

[0120] The linking material 73 of the linking layer 72 with which thelayer 136 of the conductor elements 134 is clad is, in one embodiment,identical to the linking material 76 with which the insulating leaf 74is coated.

[0121] In another version, the linking materials 73 and 76 arechemically and thermally compatible with a view to optimising theirspecific function. The material 76 is accordingly chosen to give a goodconnection with the body 19, and the linking element 73 is chosen togive good filling qualities, improved by the presence of the linkingelement 76.

[0122] The structural element 174 may also be impregnated with thelinking material 76. Thus, where the structural element 174 is of fabricor is an equivalent non-fabric element, the linking material 76 overliesits faces and penetrates at least partly between the fibres of which thestructural element 174 consists.

[0123] The linking materials may for example comprise a polymer.

[0124] The polymer may be of the thermosetting type which retains itsmechanical characteristics after being polymerised, at least up to themaximum working temperature of the alternator 10, or it may be of thethermoplastic type, the melting point of which is higher than themaximum working temperature of the alternator 10.

[0125] Given that the linking material 73 coats the conductor elements134 which are coated with the layer 136 of electrically insulatingmaterial, the step of impregnating the electrical windings 23 and 62, inthe process for making the stator 12 and rotor 13 of the alternator 10in the state of the art, is eliminated, which enables the manufacturingtime of the alternator to be reduced by several minutes or even severaltens of minutes.

[0126] The use of varnish gives rise to emissions of pollutant vapour,in particular while it is being heated. The use of different linkingmaterials 73, 76 on the coated conductor elements 134 enables the use ofvarnish to be eliminated and enables polluting emissions into theatmosphere to be reduced or even eliminated.

[0127] In the remainder of this description, the linking material 73 ofthe layer 72 and the linking material 76 will be taken to be identical.

[0128] The method of manufacturing the alternator 10 accordinglyproposes that the step of winding the coated and clad electricallyconductive wire be followed by a step of changing the state of thelinking material which causes it to become softened or to melt, in orderat least partially to fill the interstices 140 that exist between theadjacent portions of the conductor elements 134, and which then cause itto solidify once more and connect the adjacent portions of the conductorelements 134 together.

[0129] The step of changing state corresponds to a modification of thestructure of the linking material, that is to say a movement of some ofthe atoms of which it consists, with respect to each other.

[0130] In a first embodiment of the invention, the step of changing thestate of the material comprises a step of heating the linking layer 72to a curing temperature which is higher than or equal to the meltingpoint of the linking material, so as to cause it to melt or soften inorder that it flows or runs whereby to fill, preferably almost entirely,the interstices 140 that exist between the adjacent portions of theconductor elements 134.

[0131] The heating step is followed by a cooling step, in the course ofwhich the linking material sets or solidifies once more.

[0132] The hardening or solidifying temperature of the linking materialis the temperature starting from which the structure of the material ismodified whereby the material permits the elements with which it is atleast partially in contact to become connected.

[0133] Thus, where the polymer is of a thermosetting type, itsreticulation temperature will be called the hardening temperature in theremainder of this description and in the Claims.

[0134] Also, where the polymer is of a thermoplastic type, its meltingpoint will be called its hardening temperature in the remainder of thedescription.

[0135] Where the linking material is a polymer, the heating and coolingsteps permit its polymerisation and solidification, which ensure therigid linking of the adjacent coated conductor elements 134 between andwith the insulating leaf 74, which is preferably a conductor of heatlike the resin 50 so as to evacuate still more heat.

[0136] Where the insulating leaf 74 is coated with a linking material 76such as a polymer, the steps of heating to a temperature greater than orequal to the hardening temperature of the linking material 76, and ofcooling, enable it to become connected to the body 19 of the stator 13and enable its connection with the adjacent portions of the coatedconductor elements 134 to be reinforced.

[0137] Since the linking material is spaced apart at substantiallyregular intervals on the layer 136 of electrically insulating materialand on, and/or in, the structural element 174, its melting or softeningduring the rise in temperature leads to filling, preferablyhomogeneously, of the interstices 140 that exist between the adjacentportions of the coated elements 134, and between the adjacent portionsof the coated elements 134 and the insulating leaf 74. Thus, after thelinking material has been heated to a temperature greater than or equalto the hardening temperature of the linking material 76, during itscooling and solidification, the adjacent portions of the element 134 andthe insulating leaf 74 are strongly joined together and form a rigidwhole. The leaf 74 can therefore be made thin.

[0138] The insulating leaf 74 and the layer of electrically insulatingmaterial are of course so selected as to be resistant to the heatingstep.

[0139] The linking material then covers the winding 23, preferablyintegrally, thereby protecting it against pollutants from outside suchas dust. It also ensures that the elements 134 are mechanically held andstiffened.

[0140] The linking material also gives improved conduction of heat,which is favourable in combination with the thermally conductive resin50 in accordance with the invention.

[0141] The face of the insulating leaf 74 which is in contact with thewall of the axial slot 25 may be covered with the linking material 76.Thus, after heating of the linking material 76 to a temperature greaterthan or equal to the hardening temperature, cooling and solidificationof the linking material 76 causes the body 22 of the stator 12 and theinsulating leaf 74 to become strongly connected together and to form arigid whole.

[0142] The invention also proposes, in conjunction with the coolingstep, to reform in a predetermined manner the electrical windings 23and/or 62 by means of a forming tool 78 which exerts a force on at leastone zone of a winding 32, 62 in such a way as to deform it, Thus, whenthe cooling step has finished, the electrical windings 23 and/or 62 havea predetermined form which is irreversible at the working temperaturesof the alternator 10.

[0143] The application of force on at least one zone of a winding 23, 62may with advantage start before or during the heating step, to lastuntil setting or solidification of the linking material 76.

[0144] Thus, at the end of the winding step, the stator 12 is placed ina forming tool 78 shown in FIG. 10.

[0145] The forming tool 78, which is preferably made of a thermally andelectrically insulating material, is symmetrical with respect to atransverse mid-plane P. In the remainder of this description only theleft hand part of the forming tool 78 will be described with respect tothe mid-plane P, and with reference to FIG. 10.

[0146] The forming tool 78 comprises a first fixed external peripheraldie 80 in which the body 19 of the stator 12 is centred. A second,internal, die 82 is movable in a radial direction. The first die 80 isin two parts so as to come into contact with the ends of the body 19 andto immobilise the latter axially.

[0147] The second die 82 enables a force to be exerted on the annularaxial face 84 of the ear 39. It then compresses the portions of thecoated and clad electrical conductor elements 134 that constitute theear 39, against the internal faces 86 of the first die 80 as shown inFIG. 11. This second die 82 is also in two parts, which are movableradially with respect to each other in opposite directions.

[0148] Subsequently, the linking material is heated to a temperaturegreater than or equal to its hardening temperature in such a way as tocause it to melt or soften, and to harden or polymerise, in particularwhere the material is a polymer. Putting the ears 39 associated with thefilling of the interstices 140, in particular by the linking material 73of the linking layer 72, under stress, enables the portions of theelements 134 to be clamped as shown in FIG. 9, and gives modification ofthe outside dimensions of the ears 39 of the stator 12.

[0149] The form of the ear 39 then corresponds to its optimum form whichenables the size of the stator 12 to be minimised in the alternator 10,and accordingly enables the size of the latter to be reduced.

[0150] During the heating and/or cooling steps, the optimum form of thestator 12 is fixed in a way that is not reversible at the workingtemperatures of the alternator 10.

[0151] Thus, the exact dimensions of the stator 13 are determinedprecisely, and they are reproducible in quantity production.

[0152] The second die 82 then ceases to exert a force on the ear 39, andthe forming tool 78 is then opened so that the stator 12 can be removed.

[0153] Control of the dimensions of the stator 12 enables dangers offrictional contact between the portions of the coated electricalconductor elements 134 on the casing 14 of the alternator 10 to beeliminated, and therefore also eliminates wear of the layer 136 anddangers of short circuits occurring.

[0154] It will be appreciated that the ears 39 may come very close tothe front and rear bearings, respectively, of the casing 12, with theiropenings, by virtue of the second dies 82 of FIGS. 10 and 11. Thisenables the size of the casing 14 to be reduced, and therefore savesmaterial as well as reducing size. All combinations are of coursepossible, with at least one of the windings of the stator 12 and rotor13 being clad with a linking layer 72. The rotor 13 may, in anotherversion, be a projecting pole rotor and have more than one winding.

[0155] Similarly (FIGS. 12 and 13), the outside dimensions of thewinding 62 of the rotor 16 are determined by a forming tool 93. Thisforming tool 93 accordingly also comprises a first die 95 in two parts,and a second die 98, which this time is radially on the outside, beingin two parts which are movable radially with respect to each other, thistime along the axis of the shaft 15.

[0156] The first die 95 immobilises the core 67, with its parts disposedon either side of the core 67 in contact with the axial ends of thelatter. The first die 95 consists of two transverse plates which aredisposed on either side of the core 67. These plates have a thickenedportion on their radial periphery for the purpose of centring the core67 and defining a clearance between the plates and the winding.

[0157] The forming tool is thus able with advantage to give a particularform to the winding 62 so that the latter will be adjacent to the claws68, 70 and the plates 64, 66. The second die 98 is accordingly in twoparts, each of which has a hollow internal form, V-shaped in this case,so as to increase the size of the winding 62 and therefore the powerfrom the machine. This is made possible due to the presence of the resin50 provided in accordance with the invention, which enables heat to beevacuated and therefore the pads 34 and the seal 46 to be protected.

[0158]FIG. 12 shows the winding 62 of the rotor 16. Its annular outerperipheral face 90 is convex, and in this example it has a V-shapedprofile, though in another version it may be barrel-shaped to increasethe volume of the winding 23. In addition, the winding 62 has rebates 92which are made by the forming tool during the heating step and/or thecooling step, the tool being movable radially so as to optimise the sizeof the winding 62. In this connection, the rebates 92 permit the claws68 and 70 of the plates 64 and 66 to pass. Thus the volume of thewinding 62 can be increased without the total size of the rotor 13 beingmodified. In this way the output of the alternator 10 is increased.

[0159] The foregoing process also permits elimination of the windingwire which a conventional rotor carries for supporting the winding 62,as well as increasing the size of the winding. In this connection,during the winding step, the coated and clad electrical conductorelement 134 can be guided transversely by the two transverse plates 94and 96 which determine the width of the winding 62, as shown in Figure13. The two transverse plates 94 and 96 hold the coated and cladelectrical conductor element 134 until the end of the cooling step,after the linking element 76 has been heated to a temperature higherthan, or equal to, its hardening temperature. The second die 98 exerts aradial force on at least one axial annular zone of the winding 62, so asto deform it whereby to determine its external form, and in particularits diameter. The transverse plate 94, 96, together with the die 98, arethen withdrawn axially.

[0160] Similarly, it is possible to deform at least one of the zones ofat least one of the ears 39, so as to determine its external form.

[0161] A radial annular zone of the winding 23 may be deformed in such away as to produce a hollow the form of which is complementary to anaxial element (not shown) which extends, on an internal face of atransverse wall of the casing 14, towards the stator 12. Such a recessthen enables the axial dimensions of the alternator 10 to be reduced,and therefore enables its overall size to be reduced.

[0162] The winding 62 in this example is formed directly on the core 67.The heating and cooling steps enable the linking material to connect thewinding 62 to the core 67.

[0163] The winding 62 may also be formed on an intermediate member fromwhich it is separated after its linking material has hardened. It isthen assembled by being clamped on the core 67.

[0164] Elimination of the winding body firstly enables the number ofcomponents of the rotor 13 to be reduced, which reduces itsmanufacturing cost, and also increases heat transfer between the winding62 and the outside, thereby increasing the output of the alternator 10.

[0165] The increase in heat transfer also reduces the need to cool thealternator 10, and consequently enables the dimension of the coolingblades of the front fan 102 and rear fan 104 shown in FIG. 1 to bereduced, or even enables at least one of these fans, namely the frontfan 102 and rear fan 104, and in particular the front fan 102, to beomitted.

[0166] Elimination of the winding body also enables, either the volumeof the rotor 13 to be reduced while retaining the same power for thealternator 10, or the power of the alternator 10 to be increased byincreasing the dimensions of the winding 62 while retaining the volumeof the rotor 13. This power increase is possible due to the thermallyconductive resin 50 provided by the invention.

[0167] The rear ear 39 may be longer than the front ear 39.

[0168] In order to reduce or eliminate the dangers of occurrence ofshort circuits between the winding 62 and core 67, and/or to improve theconnection between them, it is of advantage to interpose between thesetwo elements a leaf 100 of electrically insulating material similar tothe insulating leaf 74 of the stator 13. The leaf 100 of electricallyinsulating material is thinner than the winding body of the prior artand is preferably coated or impregnated at least partially with alinking material which may be identical with the linking material 76.Preferably, the two faces of the leaf 100 are coated with a linkingmaterial in such a way that the linking material also connects thewinding 62 and core 67 together. The linking material for the leaf 100is then preferably of the thermoplastic type, having a melting pointwhich is higher than the maximum working temperature of the machine,though it may be of the thermosetting type with the advantage that thisenables the reliability of the machine to be increased. As mentionedabove, the linking material is a polymer.

[0169] Preferably, the leaves 74, 100 are thermally conductive so as tofavour evacuation of heat towards the body 19 and core 67 respectively.These leaves are thin.

[0170] In a modified embodiment, the method enables the volume occupiedby the windings 23 and 62 to be reduced, which reduces their volume. Inconsequence, it reduces the emission of wind noise when the alternator10 is working.

[0171] The stiffness of the linking material 73, 76 which is used ispreferably smaller than that of the varnish which is used in the stateof the art. This enables the thickness of the assembly consisting of atleast one of the windings 23, 62 and the elements to which it isconnected by the linking material 73, 76 to be reduced, which, inparticular, reduces magnetic noise emitted by the alternator 10 whileresisting mechanical stresses, in particular those due to vibration.

[0172] In addition, the linking material 73, 76 which is used ispreferably insensitive to temperature variations within the range ofworking temperatures of the alternator 10. Thus, the level of magneticnoise emitted by the alternator 10 is substantially constant when thealternator 10 is operating.

[0173] The process also enables variations in the dimensions of thewindings 23 and 62 of the stator 12 and rotor 12 to be reduced. It isthus possible to reduce working clearances between the winding 62 andthe plate 64, 70 and the claws 68, 70 respectively, together with theclearances between the stator 13 and the fans 102, 104 respectively. Inthis way, the clearances are made small.

[0174] The process also enables working clearances that exist radiallyand axially between the ears 39 of the stator 13 and the casing 14respectively to be reduced.

[0175] Thanks to the above mentioned process, the overall size of thealternator can be reduced but with an increase in power and goodevacuation of heat by virtue of the resin provided in accordance withthe invention.

[0176] Hardening of the linking material is obtained by the heating stepwhich can consist in heating the linking material by stoving, so as tobring its temperature up to a temperature greater than or equal to itshardening temperature.

[0177] In a modified version, the heating step consists in heating thecoated and clad electrical conductor element 134 by Joule effect, so asto bring the temperature of the linking material to a temperaturegreater than or equal to its hardening temperature. The temperature mustbe high enough, and the heating step must last sufficiently long, forthe linking material 76 with which the insulating leaf 74, 100 is coatedalso to attain its hardening temperature. This is for example achievedby causing a current to flow in a sufficiently high intensity in theelectrical conductor of the winding 23 and/or 62 to cause heating totake place. The temperature of the conductor element must of course inall cases remain lower than a maximum temperature, so as not to damagethe layer of electrically insulating material 136.

[0178] This increase in power of the machine makes it necessary toreform the rectifier unit 1.

[0179] Thus, in FIG. 14, part of the rear bearing 16 can be seen withits peripheral flange formed with openings 5 and its radial plate 3 alsoprovided with openings, one of which has the reference numeral 7 in FIG.7.

[0180] The unit 1 includes a plurality of positive diodes 8 supported bya metallic heat dissipater 9 in the form of a plate, together with aplurality of negative diodes 10 carried by the plate 3 of the rearbearing 16. In this example, three positive diodes 8 and three negativediodes 10 are provided.

[0181] Each of the diodes 8, 10 has a cylindrical body and tails as canbe best seen in FIG. 7. These diodes are mounted in head-to-toerelationship in order to reduce overall axial size.

[0182] The negative diodes 10 are force-fitted by means of their body,which is knurled for that purpose, into holes in the plate 3 in thebearing 16, and in a zone that surrounds the openings 7.

[0183] The tails 111 of the negative diodes 10 pass through holes 111′formed in the plate 9.

[0184] The positive diodes 8 are force-fitted by means of their bodiesin holes 8′ formed in the plate 9. The tails of the positive diodes passthrough the openings 7 in the plate 3 of the bearing 16, as can be seenin FIG. 7. The plate 9 is of mouldable material, and in this example itis made of aluminium. The plate has the general form of an annularsector.

[0185] The plate 9 is separated from the plate 3 of the bearing 16 bymeans of a plate 113 of electrically insulating material, which in thisexample is a plastics material moulded in situ on an assembly of flatelectrical conductors. The plate 113 has the general form of an annularsector.

[0186] The plate 9 is perforated and includes a large number of ribs118, 119 in the form of fins.

[0187] A passage aperture 120 for cooling air is preferably formedbetween each pair of adjacent fins 118, 119.

[0188] Some of the fins 118 extend to the outer periphery of the plate9.

[0189] Two positive diodes 8 are fitted close to the outer periphery ofthe plate 9.

[0190] The diodes 8 which are disposed close to the outer periphery ofthe plate 9 are located substantially on the same pitch circle as theholes 111′ of the diodes 10 and the passage holes 115′ for the screwsfor fastening the plate 9 or plate 3.

[0191] The third diode 8 is fitted close to a thickened mounting portionof a threaded portion 117 which serves as a terminal for connection tothe positive terminal of the battery of the vehicle.

[0192] A voltage regulator 116 and the brush carrier with the referencenumeral 200 in FIG. 14 are also provided.

[0193] The regulator 116 is of the same type as that described in thedocument FR-A-2 780 577, and accordingly comprises a sub-assemblyincluding a sub-strate on which at least one elementary electroniccomponent is mounted, such as a chip other than an integrated circuit.The sub-assembly includes, in one embodiment, a plurality of elementaryelectronic components and a plurality of integrated circuits.

[0194] The sub-assembly includes means for mounting the brushes, and inone embodiment it is accordingly integrated with the brush carrier 200.

[0195] For more detail, reference should be made to the said document,the elementary electronic component being connected to metallic tracks,being mounted in an orifice of the substrate.

[0196] The fins 118, 119 project at right angles to the upper surface ofthe thermally conductive plate 9.

[0197] The middle positive diode 8 is located between two long fins 118.

[0198] As is clearly shown in the drawings, the plate is pierced betweenthe fins in the available space. The apertures 120 constitute, with theinwardly convergent radial fins 118, 119, axial cooling channels whichensure accelerated flow of cooling air aspirated by the internal fan andsubsequently passed through the lateral openings 5 of the bearing.

[0199]FIG. 17 shows the insulating intermediate plate 13, whichincludes, in a way corresponding to the support plate 9 of the positivediodes 8, passage holes 122 for the tails of the positive diodes 8,passage holes 123 for the fastening screws 115, and passage holes 124for the passage tails of the negative diodes 10, all within the outerannular zone close to its periphery, the annular portion 125 situatedfurther inwards being provided with wide apertures 126 for flow ofcooling air, the disposition of which corresponds to the apertures 120in the plate 8. Within the scope of the invention it can be envisagedthat this annular portion 125 of the insulating plate be omitted, whichreduces the size of the plate 13.

[0200]FIG. 18 shows the protective cap 27, which is distinguished by itsoptimised configuration which is perfectly adapted to the dissipater,due to the face that the part thereof which is situated above the latteris greatly perforated, only leaving narrow radial ribs 128 and anequally narrow coaxial rib 129. The large apertures 130 which arethereby obtained, which extend radially like the cooling fins 119, 118,ensure purely axial accelerated flow of the cooling air which isaspirated, and therefore optimum cooling of the rectifier unit of thealternator. It will be noted that it is only the part that defines thetransversely oriented central plate of the cap 27 that is provided withapertures, the axially oriented annular flange of the cap, which isjoined to the outer periphery of the central plate, not having anyapertures. The air therefore passes axially through the apertures 128and 120, given that the apertures 120 are in facing relationship withthe openings 7 in the rear bearing.

[0201] In all cases, the rectifier unit includes a dissipater 9 in theform of a perforated plate with radial fins, a plate 13 with connectors,and a third component which constitutes the support for the negativediodes and is defined by the rear bearing, or a plate fixed with respectto the rear bearing. There are thus three main components.

[0202] The connector 113 is interposed between the dissipater 9 and theplate 3 of the rear bearing or a plate fixed with respect to the latter.Radial channels are formed between the fins. The tails of the positivediodes are directed towards the support for the negative diodes. Atleast two of the positive diodes lie below the apertures 120.

[0203] Thanks to the radial fins and the apertures defined between themin the support dissipater for the positive diodes, accelerated, andtherefore optimised, flow of cooling air is obtained, to which theopenings formed facing each other in the bearing and in the insulatingplate constituting a connector contribute. Given that the positivediodes are disposed close to the outer periphery of the support plate,the connector may be of reduced size. It should be noted that all theopenings are so configured that they reduce energy losses whilefacilitating air flow. It should therefore be emphasised that theopenings in the cap are aligned with the fins of the dissipater thatsupports the positive diodes.

[0204] The fact that the fins 118, 119 converge inwardly enables theflow of cooling fluid, which in this case is air but which in anotherversion may be some other fluid, to be accelerated.

[0205] The arrangement of two of the positive diodes at the outerperiphery of the dissipater 9 enables the thickness of the dissipater 9to be increased at this point, creating on the latter, for example, athickened portion having a generally trapezoidal cross section. In thisway, heat is evacuated in the best possible way and the plate 9 isstiffened. Preferably, the plate 9 is made by moulding and is ofaluminium.

[0206] It will be noted that the winding 23 has several coils soarranged as to form, in this case, the three phases of the alternator.FIG. 1 shows three electrical conductors, namely one per phase. Theseconductors are connected to the flat conductors of the plate 113 throughelements 114 in the form of wire grippers which are included in the flatconductor elements.

[0207] The plate 3 has apertures for passage of the conductors of thephases, as can be seen in FIG. 7. It will be noted that shouldered,electrically insulating sleeves are interposed between the screws 115and the holes 115′ so as to prevent any short circuit. Some of thescrews 115 have a threaded portion for fastening to the cap 27 bysnap-fitting.

[0208] Thus, in accordance with the invention, the alternator describedabove has a stator which is perfectly centred due to the resin, and acasing with a reduced axial size, together with a well cooled rectifierunit. The alternator is powerful within a reduced volume while beingless noisy.

1. A rotary electrical machine (10) of the type comprising a rotor (13),a stator (12) of generally cylindrical annular form surrounding therotor (13) and arranged within a casing (14) comprising a rear portion(16) and a front portion (18), which are joined together along ajunction plane (P) at right angles to the axis (X-X) of the rotor of themachine (10), wherein the external axial face (24) of the stator (12)delimits, with the internal axial face (30) of the casing (14), anannular radial space (32), and wherein the stator (12) is clampedaxially between the opposed radial engagement surfaces (36, 48) whichare formed in each of the two portions (16, 18) of the casing (14), withat least one elastically deformable element (34, 46) being interposedand compressed axially between each of the two engagement surfaces (36,48) and a portion of the facing annular radial end face (20, 22) of thestator (12), characterised in that at least part of the radial annularspace (32) contains elastically deformable thermally conductive resin(50) which is interposed radially between the casing (14) and the stator(12), whereby to effect radial mechanical decoupling between the stator(12) and casing (14), and whereby to dissipate heat energy from thestator (12) to the casing (14).
 2. A rotary electrical machine (10)according to the preceding claim, characterised in that only the frontportion (18) of the casing (14) contains the thermally conductive resin(50).
 3. A rotary electrical machine (10) according to claim 1,characterised in that an elastically deformable flat annular seal (46)is interposed axially between the annular front radial end face (22) ofthe stator (12) and the engagement surface (48) formed in the frontportion (18) of the casing (14).
 4. A rotary electrical machine (10)according to claim 1, characterised in that a set of elasticallydeformable pads (34) are spaced apart circumferentially and compressedaxially between the rear annular radial end face (20) of the stator (12)and a portion of the engagement surface (36) defined in the rear portion(16) of the casing (14).
 5. A rotary electrical machine (10) accordingto the preceding claim, characterised in that each pad (34) includes apositioning lug (38) in the form of a dovetail which is received axiallyin a complementary seating (44) formed in the rear portion (16) of thecasing (14).
 6. An alternator (10) for a motor vehicle, characterised inthat it is made in accordance with any one of the preceding claims. 7.An alternator (10) according to claim 6, characterised in that it isadapted to work alternately as a starter motor or as an alternator. 8.An alternator (10), characterised in that the rotor (13) includes awinding (62) and two plates (64, 66) having claws (68, 70), in that thewinding (62) is disposed between the plates (64, 66) and the claws (68,70), and in that the winding (62) is adjacent to the claws (68, 70) andplates (64, 66), in such a way that there is a slight clearance betweenthe claws (68, 70) and the plates (64, 66).
 9. An alternator accordingto claim 8, characterised in that the rear portion (18) carries arectifier unit (1) that includes negative diodes (10) carried by therear portion (18) and positive diodes (8) carried by a support plate(9), in that the support plate (9) has a large number of ribs (118, 119)in the form of fins, and in that a passage aperture (120) for coolingair is provided between each pair of adjacent fins.
 10. An alternatoraccording to claim 9, characterised in that it includes a cap (27) whichhas corresponding radial apertures at the level of the fins (118, 119)of the plate (9).